Transporting very large equipment such as earthmoving equipment used on mine sites, particularly large tracked vehicles, require specially designed large flat bed trailers. Conventional large rear-loading trailers have a large number of wheels at their rear ends. Because of the large number of wheels, their diameter can be relatively small to facilitate loading. However, the lip of the loading deck is still usually high enough off the ground to make loading of some large vehicles difficult. Large front loading trailers are also known. These trailers typically have wheels located at their rear ends and liftable front ends. The liftable front ends are designed to be lowered to engage the ground so as to present a minimal step or ramp up on to the trailer bed for loading.
Special hitch arrangements, referred to as gooseneck hitches have been developed to allow lifting and lowering of such trailer ends. These hitches are designed so that the gooseneck can be removed from the trailer leaving the front end clear for loading.
It is known to use goosenecks having hydraulic rams arranged through linkages to provide a force couple to the end of a trailer to cause relative rotation of the platform and gooseneck. This relative rotation raises/lowers the trailer end. Existing hitch assemblies have a number of problems. For instance with the existing hitch assemblies, goosenecks typically have a hook which engages a pin laterally disposed with respect to the front end of the trailer. As the trailer end is raised there is rotational movement between these two components. The friction associated with this rotational movement reduces the efficiency of the lifting process and causes wear.
A further problem with existing hitch arrangements is that as the trailer end is raised, the trailer is pushed away from the tow vehicle. If brakes are applied to the wheels of both the tow vehicle and the trailer, this horizontal movement can cause significant stresses in the hitch assembly and trailer.
Other problems with the existing hitch assemblies include locking of the hitch in a raised position for transport. With some existing designs it is necessary to insert compression blocks to take the load off lifting joints and components before transport can occur. With other designs there are no locking mechanisms at all and a leakage or bypass in the hydraulic cylinder or valves can cause the trailer to drop.
A further problem with many existing designs is that the placement of the hydraulic cylinders is such that it is difficult to maintain them.
Another problem with some existing designs is that separate mechanisms are required to transmit forces caused by braking and/or traction.
Finally with many hitch arrangements it is difficult to align the gooseneck with the trailer end.
It is an object of the invention to overcome at least some of the above problems.